Can/Should I Use an Asynchronous Controller Here? (ASP.NET MVC 3)

Question

I have this [HttpPost] action method:

[HttpPost]
public ActionResult AddReview(Review review)
{
   repository.Add(review);
   repository.Save();
   repository.UpdateSystemScoring(review.Id); // call SPROC with new Review ID.
   return View("Success", review);
}

So, basically a user clicks a button, i add it to my database (via Entity Framework 4.0), save changes, and then i call a stored procedure with the identity field, which is that second last line of code.

This needs to be done after the review is saved (as the identity field is only created once Save is called, and EF persists the changes), and it is a system-wide calculation.

From the user point of view, he/she doesn't/shouldn't care that this calculation is happening.

This procedure can take anywhere from 0-20 seconds. It does not return anything.

Is this a candidate for an asynchronous controller?

Is there a way i can add the Review, and let another asynchronous controller handle the long-running SPROC call, so the user can be taken to the Success page immediately?

I must admit (partially ashamed of this): this is a rewrite of an existing system, and in the original system (ASP.NET Web Forms), i fired off another thread in order to achieve the above task - which is why i was wondering if the same principal can be applied to ASP.NET MVC 3.

I always try and avoid multi-threading in ASP.NET but user experience is the #1 priority, and i do not want the page timing out.

So - is this possible? Also happy to hear any other ideas. Also - i can't use triggers here, don't really want to go into too much detail why - but i can't.

Answer 1

I would fire a new thread (not from the thread pool) to perform this task and return immediately especially if you don't care about the results. Asynchronous controllers are useful in situations where most of the time is spent waiting for some other system to complete the task and you once this system completes the task your application is signaled to process the result. During the execution of the task no threads are consumed from your application. So in your scenario this task could be performed by SQL Server using the async versions of the BeginRead methods in ADO.NET. You could use this if you need the results back. If you don't firing a new thread would work just fine as before.

Answer 2

I think asynchronous controllers are more for things where the request may take a long time to return a response, but the main thread would spend most of that time waiting for another thread/process. This is mostly useful for ajax calls rather than main page load, when it is acceptable to just show a progress indicator until the response is returned.

I use a separate queueing system for this type of task, which is more robust and easier to work with but does take a bit more work to set up. If you really need to do it within the ASP.net process, a separate request is probably the best option, though there is some potential for the task not to run - for example I'm not sure what happens if the connection drops or the app pool recycles while an async task is running.

Answer 3

Since the scoring system takes so long to run I would recommend using a scheduled task in SQL Server or Windows to update the scores every x amount of minutes. Since the user doesn't know about the request it don't matter to run immediately.

You could add the ID's to a queue and process the queue every 30 minutes.

Otherwise if there is a reason this needs to be run immediately you could do an asyc call or see if you could trim some fat of the stored proc.

Answer 4

I have a very similar system that I wrote. Instead of doing things synchronously we do everything asynchronous using queues.

Action -> causes javascript request to web server
   |
Web server puts notification on queue
   |
Worker picks up message from queue and does point calculation
   |
At some point in future user sees points adjusted

This allows us to be able to handle large amounts of user load and not need to worry about this having an adverse affect on our calculation engine. This also means that we can add more workers to handle larger load when we have large load and can remove workers when we don't have a large load.